As known, in the absence of satellite assistance (for example of the GPS type), the navigation function of a projectile is first implemented upon an initialization phase consisting in determining the attitude and the position of the projectile at an initial instant. Such an initialization phase is then followed with a propagation phase consisting in determining the position and the attitude of the projectile upon the flight through on-board measurement instruments within the projectile (for example, accelerometers, gyrometers, magnetometers, . . . ).
Now, in the case of a projectile shot from a gun, the on-board measurement instruments are unavailable during the gun shot as a result of very high lateral and axial accelerations (saturating the inertial unit of the projectile) and the environment of the gun (including the presence of ferromagnetic masses making the magnetometers of the projectile unusable). Consequently, the initialization of the navigational function cannot be carried out, the complete attitude of the projectile remaining then undetermined at the outlet of the muzzle of the gun.
For overcoming such an absence of measurement during the gun shot, it is known to determine the aerodynamic speed of the projectile from the reference trajectory at the outlet of the gun shot. However, such a determination is very approximate, as the actual trajectory of the projectile differs from the reference trajectory, making an accurate navigation of the projectile very difficult.
It is also known to estimate, in the course of flight, the attitude of the projectile using on-board magnetometers through measurement of the terrestrial magnetic field. However, the accuracy of the measurements being carried out remains limited and no information regarding the aerodynamic speed the projectile is however available.
Moreover, for a projectile supposed to be very stable and provided with gyrometers and accelerometers, it is known to measure the gravity with such on-board measurement instruments for estimating the attitude and the aerodynamic speed of the projectile during a ballistic flight phase. However, such an estimation of the aerodynamic speed could only be carried out upon the ballistic flight phase of the projectile. Moreover, the attitude estimation is strongly altered by any incidence uptake of the projectile (for example, as a result of the wind).
Furthermore, when the measurement instruments on-board the projectile are of a mean or bad quality, the inaccuracy on the estimation of the attitude of the projectile makes the navigation of the projectile very bad on a high flight duration.